ML20055E531

Forwards Request for Addl Info Re Facility Control Assembly Action Program,Per 900607 Control Element Assembly Failure at Maine Yankee.Confirmation of NRC Understanding That Util Intends to Implement C-E Plan Also Requested

ML20055E531
Person / Time
Site:	Calvert Cliffs
Issue date:	07/06/1990
From:	Capra R Office of Nuclear Reactor Regulation
To:	Creel G BALTIMORE GAS & ELECTRIC CO.
References
TAC-66457, NUDOCS 9007120105
Download: ML20055E531 (6)

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" July:6, 1990 Docket Nos. 50-317 and 50-318:

Mr. G. C. Creel-

. Vice President -' Nuclear Energy Baltimore Gas;& Electric Company Calvert Cliffs iNuclear Fower Plant MD Rts. 2 & 4 Post Office-Box 1535 Lusby, Maryland 20657 y *

SUBJECT:

GENERIC IMPLICATIONS AND-RESOLUTION OF CEA~ FAILURE AT MAINE YANKEE FOR CALVERT CLIFFS, UNIT NOS 1 AND 2 (TAC NO. 66457)

On June 7, 1990, while conducting cold functional testing of the control

' element assemblies (CEAs) following the cycle 12 refueling outage at Maine Yankee, one CEA could not be fully inserted in the core. Subsequent inspection of the CEA revealed that the end cap was missing from the center CEA finger, the lower stainless steel spacer and boron carbide pellets had fallen out of the center finger and an axial crack existed at the. lower end. The upper stainless steel spacer was cocked in the bottom of the CEA finger and was causing the center CEA finger to bind against the guide tube. The CEA could

not be fully inserted in the core during cold functional testing due to interference from boron carbide pellets that had fallen into the center CEA

. guide tube.

2 On June 25, 1990, the NRC staff met with the Combustion Engineering Regulatory ResponseGroup(CERRG).todiscussthegenericimplicationsandproposed resolution of the CEA failure that occurred at Maine Yankee. The CERRG concluded that the CEA failure was most likely due to irradiation assisted stress corrocion cracking (IASCC). The CERRG also concluded that the failure mechanism was only applicable to the older Combustion Engineering (CE)'CEA 9 designwhichdidnothaveanabsorberplug(otherthanboroncarbidepellets) at the bottom of the center CEA finger. In order to resolve this issue, the CERRG proposed specific Action Programs for each affected licensee. The CERRG submitted its' report to the NRC addressing this issue by letter dated June 26,

1990.

It is-our understanding that Calvert Cliffs 1 currently does not have any of the old style CEAs installed in the reactor core and that you do not plan to use any old style CEAs in the future. Therefore, this problem is not applicable 9

to Calvert' Cliffs 1 and no specific actions are required. Please contact us if

our understanding regarding this matter is not correct.

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Mr. G. C. Creel '

i .g It is our understanding that Calvert Cliffs 2 currently has 68 CEAs which are vulnerable to the IASCC' failure mechanism discussed above and that you intend-to implement the Action Program which is included as Enclosure 1 to this letter. Enclosure 2 is a request for additional information regarding your Action Program. By July 20, 1990, you are requested to- provide your response'

- to our request for additional information and to confirm our understanding that you intend to implement the CERRG Action Program for Calvert Cliffs. If you have-any questions regarding this request, please contact Mr. D. Mcdonald of-my staff at (301) 492-1408.

The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under-

' Pub. L.-96-511.

S',ncerely,

>R!GINAL SIGNED BY:

Onofel b 0 & hms<t w o f Robert A. Capra, Director Project Directorate I-1 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation

Enclosures:

As stated cc w/ enclosures:

See next page

' Distribution:

Docket File EJordan NRC/ Local PDPs ACRS(10)

PDI-1 Reading Plant File JPartlow JLinville SVarga RJones BBoger JTatum RACapra y RHermann CVogan- LPhillips DMcDonald CYCheng OGC

• SEE PREVIOUS CONCURRENCE PDI-1 PDI-1 (D PAD 5 SRXB- EMCB h

PDI-1 L

• CVogan *DMcDonald:rse \J tufn *LPhillips *RHermann RACaprti 7/05 90 7/05 /90 7/ '.,/90 7/05/90 7/06 /90 7/f/90 DOCUMENT HAME: CALVERT CLIFFS 2

, ~ Mr. r,..C. Creel Baltimore' Gas & Electric Company-Calvert Cliffs Nuclear Power Plant Cc .

Mr. William T., Dowen, Dresident Calvert' County Board of Mr. Joseph H. Walter Commissioners . Engineering Division Drince Frederick, Maryland 20678 Dublic Service Commission of Maryland American Duiliing 231 E. Ral+".. ore Street D. A. Brune, Esq. Baltimore, Maryland 21202 3486.

General Counsel

' Baltimore Gas and Electric Company D. 0. Pox 1475' Ms. Kirsten A. Burger, Esq.

Aaltimore, Maryland 21203 Maryland .Deeple's Counsel American Building, 9th Floor Mr. Jay E silberg, Esq. 231 E. Baltimore Street Baltimore, Maryland 21202 Shaw, kittman, Potts and Trowbridge-2300 N Street, NW Washington, DC 20037 Ms. Patricia Birnie '

Co-Director Maryland Safe Energy Coalition Ms. G. L. Adams, ticensing P. O. cox 902 Columbia, Maryland 21044 Calvert Cliffs Nuclear Power Plant MD-.Rts 2 & 4, p. O. Box 1535

.Lusby, Maryiand 20657 Resident inspector c/o ll.S. Nuclear Regulatory Commission P. O. aox 437 Lusby, Maryland 20657 Mr. Richard McLean Administrator - Radioecology Department of Natural Resources 580 Taylor Avenue Tawes State Office Building PPER 83 Annapolis, Maryland 21401 Qegional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19d06 l

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ENCLOSURE 2 REQUEST FOR ADD!r10NAL INFORMATION RE:

CALVERT CLIFFS E CEA ACTION PROGRAM

11. It is our understanding that additional evaluation and analyses are being 1 performed relative to the Maine Yankee CEA failure.

Provide a description of the additional-information being developed and what impact this -information may have on your Action Program.

2. During the Cycle 9 refueling outage, you performed ECT inspection of the 4 old sty'le CEAs. While your inspection techniques may detect axial cracks in the CEA' fingers, it is unlikely that you would detect any circumferential cracks that'may exist in the end cap welds. Because crack initiation in l the end cap weld can not be dismissed as a possible failure mechanism, this matter must be addressed.  :

Provide your assessment and resolution of this concern, including any_  ;

proposed changes'to your Action Program to account for uncertainties. '

3. The Action Program defines "old CEA" as one with no AG-IN-CD slug in the center finger and that has achieved high exposure. Recently, CEA degradation was identified associated with one Maine Yankee CEA with only 2732 EFPD-exposure. Additionally, one Maine Yankee CEA with only 3415 EFPD exposure failed with loss of end cap and absorber material from the center finger and loss of full insertion capability.

a. Define how many EFPD constitute "high exposure" and clarify your plans and criteria for replacement of old style CEAs.

.b. Provide justification for continued operation with any of the old style CEAs beyond the next refueling outage.

L c. Provide information on the availability of replacement CEAs and the ..

precurement lead time required to replace all old style CEAs. '

-4.

. Your Action Program does not require the old style CEAs to be exercised L following rod drop testing to verify that the CEAs continue to be

l. functional. Rod drop testing creates additional stresses'in the CEA L which could lead to failure. Currently, there is no assurance that all L of the old style CEAs are functional.

l l Provide your assessment and resolution of the consideration discussed

!' above, including any proposed changes to your Action Program to account L

for uneartainties. I l

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, 5. YourproposedActionProgramprovidesforextended' operation (approxi-mately 2 years) with no. inspection or functional testing' of the old CEAs in the Cycle 9 core unless there is a reactor trip'or cold shutdown'during the operating cycle. Your M tification appears to be predicated on experience with one CEA whicn may have operated for more than one cycle without functional failure after a crack had initiated. Since the postulated CEA failare mechanism is IASCC and' vulnerability is very sensitive to variattons in material properties and composition .

applicability o' tM previous experience to the CEAs currently residing in the Calvert Cliffs 2 core has not been established.

Further, the propagation rate of IASCC is known to be a function of stress level (including residual stresses), vulnerability of the specific material and the operating environment. Additionally, the vulnerabilit) to cracking is increasing during plant operation due to continuous radiation exposure and continued swelling of boron carbide pellets. The advanced exposure of the old CEAs currently installed in the Calvert Cliffs 2 core makes the CEAs more vulnerable to IASCC and crack propagation than old CEAs that were installed during previous' operating cycles . Although no cracks were found by eddy current test ECT inspections during the Cycle 9 refueling outage, there is no assurance that cracks will not develop and propagate and cause CEA failure during the operating cycle.

Provide your assessment and resolution of the considerations stated above, including any proposed changes to your Action Program to account for uncertainties.

6. In the accident analyses, the worst case CEA is assumed to be stuck in the fully withdrawn position during a postulated event. The IASCC CEA failure mechanism could result in a multiple failure of CEAs to fully' insert during the postulated event and must be considered.

Provide a comprehensive safety evaluation of the multiple rod failure event that could be postulated assuming that old CEAs are subject to the Maine Yankee failure mechanism. If your evaluation cannot be completed in time to support the required resp ase date, provide a description of your planned evaluation and your schedule for completion.

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